The present invention relates to a magnetic disk drive.
A magnetic disk drive is used to record information in a plurality of concentric circular tracks and reproduce recorded information by rotating a magnetic recording medium of a disk type called a magnetic disk and by means of a magnetic head placed in an arbitrary radius position on the magnetic disk.
In such a magnetic disk drive, as a system of flying the magnetic head on the magnetic disk extremely slightly, e.g. 100 nm, by using the dynamic pressure effect of air, a fixed magnetic disk drive and a magneto-optical disk drive are available. In a drive like these, a given load is mechanically applied to a magnetic head in the direction of a magnetic disk by a suspension which supports the head, and this magnetic head is flied at flying height in which a force produced by a dynamic pressure bearing and the load given by the suspension are balanced.
The magnetic head moves to an arbitrary position on the magnetic disk. However, since the speed of an air flow passing through an air bearing increases more in an outer peripheral position than in an inner peripheral position, a flying force produced by a dynamic pressure air bearing increases and flying height also increases. There is a problem that reduction in a recording density is greater closer to the outer circumference as there is a negative correlation between this head flying height and the recording density. As methods of solving this problem and maintaining the recording density uniform in inner and outer circumferences, one to keep the flying height constant by providing an angle between the magnetic head and the air flow and one to attain the same purpose by adding some effective changes to the form of the bearing are known. However, by the former method variations in the flying height cannot be reduced so much though the air bearing section is simplified, and by the latter processing of the form of the air bearing section is difficult and besides the flying height cannot be made accurately constant.
In addition to the difficulty of making uniform the flying characteristic of a single magnetic head in every track position, it is difficult to make uniform the flying characteristics of a plurality of heads. That is, other than the air bearing section there are a great number of factors in which differences are generated, such as a suspension attaching position, a suspension load and the like, making it practically impossible to remove a difference in flying height among the heads. Thus, under the circumstances, some freedom is given to designing of a drive expecting such nonuniformity in characteristics.
As for cases where the head flying height variations due to a change with the lapse of time after the magnetic disk drive is assembled and the drive is set in an environment in which atmospheric pressure is extremely low, such as in highlands or the like, conventionally there have been no methods found to make the head flying height optimum.
The above-described magnetic disk drive in which the magnetic head is flied generally uses a method called CSS (contact/start/stop) of bringing the head into contact with the magnetic disk when the disk starts rotating and flying the head only when the number of rotations thereof increases. Since a load on the magnetic head is given by the suspension, almost the same load is applied at the time of contact as at the time of flying. As a result, there is a possibility that the magnetic disk may be destroyed by the load on the magnetic head at the time of performing the CSS. It is preferable for the load on the magnetic head to be big in order to improve stability against external disturbances, etc., at the time of flying. Generally, however, a light load of 3 to 10 grams is used so as to prevent destruction of the head.
Also, the dynamic pressure air-bearing mechanism has a sort of equivalent spring characteristic. In the case where acceleration is exerted from a source external to the drive due to a disturbance such as vibrations, therefore, the resulting shock fluctuates the flying height (i.e., the position) of the magnetic head slider. In recent years, the recording density has been increased with the increasing storage capacity of magnetic disk drives. A very low-flying structure has been developed with the flying height minimized. As a result, fluctuations of flying height due to disturbances causes an unstable write/read operation of the magnetic head for an increased error rate.
On the other hand, a method in which the magnetic head is not borne in air but kept in contact with the magnetic disk is available as a technique for increasing the recording density. A representative method is a floppy magnetic disk. A contact system has recently been employed, however, also for a fixed magnetic disk drive. In the contact system which has no fluctuations of flying height relatively stabilizes the position of the magnetic head. Nevertheless, air undesirably intrudes into a gap which is unavoidably formed between the magnetic head and the contact surface due to the fluctuations (surface roughness) of the surface of the magnetic disk.
With this reason, there are other methods by which the magnetic head is not flied but always brought into contact with the magnetic disk. Representative of them is a floppy disk and recently even for a fixed magnetic disk drive the use of this contact method has been proposed. Even in a case where the magnetic head is brought into contact with the magnetic disk, however, since air flows into spaces produced by ruggedness on a contact surface, contact surface pressure may be reduced when a sliding speed increases depending on the position of the magnetic head, the head touching may be deteriorated and S/N of a reproducing signal may be reduced. Thus, though a given pressing load is necessary for the magnetic head of a contact type, it is difficult to apply a sufficient load in order to prevent reduction in quality of the magnetic disk caused by sliding.
A load on the magnetic head is mechanically applied by a supporting spring such as a suspension and the like supporting the head. For this reason, if here are errors in manufacturing the magnetic head, the magnetic disk, etc., the load varies and this makes variations of flying height and pressure in contact surface, etc., to be big.
The contact system, like the air-bearing system, requires a certain degree of pressure load. It is necessary, however, to limit the load in order to avoid deterioration of the magnetic disk which otherwise might be caused by the sliding operation with the magnetic head. For this reason, the suspension (support spring member) for supporting the magnetic head and applying a minute load to it is very low in mechanical strength, resulting in a low resonance frequency due to the magnetic head and the suspension. Consequently, the magnetic head jumps up from the surface of the magnetic disk, especially when it is subjected to an external disturbance (a force such as a vibration having an acceleration) of a such a low frequency as to affect the mechanism of the magnetic disk and the magnetic head. The resulting increased distance between the magnetic head and the magnetic disk increases what is called the magnetic spacing, thereby making it difficult to produce a sufficient write/read signal characteristic. Also, due to the presence of fluctuations on the surface of the magnetic disk, the magnetic head is liable to jump up from the magnetic disk according as the resonance frequency due to the magnetic head and the suspension approaches the fluctuation frequency, thereby causing an unstable write/read signal characteristic.
In addition to the drive for mechanically obtaining the pressing force of the flying head, as disclosed in Japanese Patent Publication KOKAI No. 61-151839, there is available a drive for controlling flying height to be low by applying a voltage across the flying head and the disk in a device for eliminating a projection on the surface of the magnetic disk. According to this paper, the pressing force of the head increases by the application of a voltage. As to stable flying, however, no description is made in detail. A projection is supposed to be erased by a contact between the head and the disk. With the contact, however, electric charge is caused to flow across the head and the disk, making it impossible for the charge to be controlled.
Furthermore, in Japanese Patent Publication KOKAI No. 5-20824there disclosed is a drive for flying the head by giving electric charge to the magnetic head and the magnetic disk and utilizing an electrostatic repulsive force. In this case, a flying force by air is limited and thus pressure must be reduced inside the magnetic disk.
A method of measuring in real time and controlling the clearance between the magnetic head and the magnetic disk (hereinafter referred to simply as xe2x80x9cthe head clearancexe2x80x9d) is described in U.S. Pat. No. 5,153,785. This reference discloses a method of determining the head clearance in real time by measuring the field electron emission current generated by the field electron emission phenomenon between opposed metal electrodes. A method of controlling the head clearance is also disclosed, in which a fine vertical motion mechanism including a piezoelectric device is attached to an electrode 17. This control method requires a special mechanism of a piezoelectric device or the like. Further, this reference contains the description that the value of the head clearance is fed back to the control mechanism in such a manner as to control the clearance to a set value, but fails to disclose a specific solution.
The object of the present invention is to provide a magnetic disk drive in which the flying height of the magnetic head (fluctuation of the contact state or flying height) can be appropriately controlled in accordance with the position of the magnetic head on a track or the operation mode of the magnetic disk drive.
More specifically, it is the object of the invention to provide a magnetic disk drive as specified in the following:
(1) Recording density uniform in both inner and outer circumferences of a magnetic disk is to be achieved by giving a head load for obtaining specified head flying height irrespective of the position of a magnetic head;
(2) Damages to the magnetic disk are to be reduced by reducing a head load at the time of CSS or idling in the case of a flying head, or at the time of sliding in the case of a contact head; and
(3) High density recording is to be realized with optimum head flying height by giving an appropriate load to the magnetic head irrespective of errors in manufacturing a suspension, etc.
(4). When the drive is subjected to a disturbance, a stabilized write/read signal characteristic is secured by suppressing the fluctuations of the flying height of the magnetic head of the air-bearing system or by controlling such fluctuations of the contact state of the contact system as to cause the magnetic head to come away from the magnetic disk.
(5) A stabilized write/read signal characteristic is secured by suppressing such fluctuations of the contact state as to cause the magnetic head to come away from the magnetic disk or the fluctuations of flying height due to the roughness of the surface of the magnetic disk.
In the first magnetic disk drive of the present invention is characterized by comprising: a rotary magnetic disk; a magnetic head having a head slider arranged oppositely to the magnetic disk and a transducer supported by the head slider for performing recording/reproducing information to and from the magnetic disk; and voltage applying section for applying a voltage across the head slider and the magnetic disk in accordance with at least one of a track position on the magnetic disk in which the magnetic head is positioned and the operation mode of the magnetic disk drive.
According to the present invention, by applying a voltage across a head slider and the magnetic disk, electric charges of reverse codes are generated on opposed surfaces of the head slider and the magnetic disk and an attracting force in proportion to the square of a potential difference is generated. The head slider is provided with a slider surface for forming an air bearing section so that it can fly on the magnetic disk and a flying force is generated against the magnetic disk by an air dynamic pressure effect produced by the rotation thereof. In short, by applying a voltage across the head slider and the magnetic disk to give an attracting force equal to a flying force, the magnetic head is flied up to specified height.
Also, according to the invention, by applying a voltage across the head slider and the magnetic disk in accordance with at least either of the track position of the magnetic head or the operation mode of the magnetic disk drive, head flying height is properly controlled based on the track position of the magnetic head or the operation mode of the magnetic disk drive.
The preferred manners of the magnetic disk drive of the invention are as follows:
(1) By the voltage applying section, a voltage applied across the head slider and the magnetic disk is increased as the track position of the magnetic head is moved from the inner peripheral side of the magnetic disk to the outer peripheral side, a head load is given so as to obtain specified head flying height irrespective of the position of the magnetic head and thereby recording density uniform both in the inner and outer circumferences of the magnetic disk can be achieved.
(2) By the voltage applying section, a voltage applied across the head slider and the magnetic disk is decreased to 0 or very small one at the time of a contact/start/stop mode, increased at the time of a seek mode higher than one at the time of the contact/start/stop mode, increased at the time of a read/write mode higher than one at the time of the seek mode and thereby damages can be reduced by reducing a head load at the time of the CSS or idling in the case of the flying head or at the time of sliding in the case of the contact head.
Moreover, by giving an appropriate load to the magnetic head irrespective of errors in manufacturing the suspension, etc., high density recording can be realized with an optimum head flying height.
(3) By setting the upper limit of the level of a voltage applied across the head slider and the magnetic disk at 3xc3x97(xcfx89R)xc2xd (volt), the magnetic head can be surely flied on the magnetic disk, where, R is maximum track radius (m), xcfx89 is rotary angular velocity of the disk (1/s).
(4) By setting the volume of the head slider at one below 15 mm3, a big electrostatic attracting force is generated to the mass of the head slider when a voltage is applied across the head slider and the magnetic disk and thereby a stable head flying characteristic can be obtained.
(5) If the flying height of the magnetic head on the magnetic disk in a recording/reproducing mode is set below 100 nm, the head flying height can be controlled by applying a small voltage across the head slider and the magnetic disk. p1 (6) By providing current limiting section for limiting a current caused to flow between the magnetic head and the magnetic disk when the head is brought into contact with the disk, the disk and the head can be prevented from being destroyed by an excessive current.
(7) An actuator electrically connected to the head slider for moving the head slider in the radial direction of the magnetic disk is further comprised, and the voltage applying section applies a voltage across the head slider and the magnetic disk via the actuator. Since a voltage is directly applied to an actuator, it is unnecessary to provide a special wiring for applying a voltage across the magnetic disk and the magnetic head.
(8) By detecting the flying height of the magnetic head on the magnetic disk and controlling a voltage applied across the head slider and the magnetic disk based on the result of this detection, a voltage to be applied can be properly controlled.
(9) The voltage applying section applies a voltage in accordance with the flying characteristic of each of a plurality of magnetic heads.
(10) The voltage applying section applies a voltage for controlling the flying characteristic of the magnetic head across the head slider of at least one selected from the plurality of magnetic heads and the magnetic disk.
(11) The head slider includes a composite head of which recording and reproducing elements are laminated, and a skew angle between the longitudinal direction of the magnetic gap and the track direction of the magnetic disk is almost constant from the innermost circumferential track to the outermost circumferential track.
(12) Since the drive is provided with section for limiting a current to flow between the magnetic disk and the magnetic head when the head is brought into contact with the disk, the magnetic disk and the magnetic head can be electrically and mechanically protected.
(13) Current limiting section is formed of an insulating layer provided on at least either of the opposed surfaces of the magnetic disk and the head slider or constituted of a resistor inserted between the magnetic head and the voltage applying section. In the latter case where the resistor is used as the current limiting section, it is preferable that resistance value thereof is bigger than a contact resistance value when the magnetic head is brought into contact with the magnetic disk.
(14) By providing an insulating layer on at least either of the opposed surfaces of the magnetic disk and the head slider, the magnetic disk and the magnetic head can be electrically and mechanically protected, and by keeping a voltage applied across the head slider and the magnetic disk below the dielectric breakdown voltage of the insulating layer, destruction of the insulating layer by the application of a voltage can be prevented.
(15) A head pressing force for pressing the magnetic head toward the magnetic disk is applied from the suspension which supports the magnetic head. By applying a small pressing force for pressing the magnetic head toward the magnetic disk from the suspension which supports the magnetic head, even when a voltage applied 6 across the head slider and the magnetic disk is decreased to 0 or very small one, a load weight on the magnetic head and flying height thereof can be stably maintained.
(16) As a reproducing head of the magnetic head, a magnetic flux sensing type such as an MR head and the like is used.
Since a voltage is directly applied to an actuator, it is unnecessary to provide a special wiring for applying a voltage across the magnetic disk and the magnetic head.
Also, according to the invention, there is a case where the magnetic disk is provided with a plurality of magnetic heads for recording/reproducing information to and from the magnetic disk having head sliders arranged oppositely to the magnetic disk and transducers supported by the head sliders; and voltage applying section for independently applying a specified voltage across the head slider and each of the plurality of magnetic disks.
In this case, if the voltage applying section is provided with a plurality of magnetic heads, by applying different voltages across the head slider and the magnetic disk in accordance with the flying characteristics of respective magnetic heads, nonuniformity in the flying characteristics of magnetic recording media can be corrected.
If the voltage applying section is provided with a plurality of magnetic heads, by applying a voltage for limiting the flying characteristics of selected optional magnetic heads across the head slider and the magnetic disk only therein and by maintaining bigger and safer flying height in the other magnetic heads, reliability of the drive can be improved.
Also, according to the first magnetic disk drive of the present invention, there is provided a magnetic disk drive, further comprising detection means for detecting such a disturbance as to fluctuate at least selected one of the position of the magnetic head slider and the driving force of the magnetic head with respect to the mechanisms for supporting the magnetic disk and the magnetic head slider, respectively, and control means for controlling the potential difference between the magnetic disk and the magnetic head slider applied by the voltage application means and setting the magnetic head slider in a predetermined position with respect to the magnetic disk on the basis of the detection result of the detection means.
As described above, according to the invention, it is possible to apply a load for giving specified head flying height irrespective of the track position of the magnetic head and to achieve uniform recording density both in the inner and outer circumferences. Moreover, it is possible to lengthen the life of the drive and further to reduce electric consumption by reducing a head load at the time of performing the CSS, sliding and idling and thereby reducing damages to the magnetic disk.
According to a second magnetic disk drive of the invention, there is provided a magnetic disk drive comprising a rotating magnetic disk constituting a recording medium, a magnetic head slider carrying a magnetic head for writing/reproducing the information on the magnetic disk, voltage application means for applying a potential difference between the magnetic disk and the magnetic head slider, detection means for detecting such a disturbance as to cause fluctuations of at least selected one of the position of the magnetic head slider and the driving force of the magnetic head with respect to the supporting mechanisms for supporting the magnetic disk and the magnetic head slider, respectively, and control means for controlling the potential difference between the magnetic disk and the magnetic head slider applied by the voltage application means and setting the magnetic head slider in a predetermined position with respect to the magnetic disk on the basis of the detection result of the detection means.
The magnetic disk drives according to preferred manners of the invention are described below.
(1) The magnetic head includes a magnetic head for recording/reproducing information while in contact with the surface of the magnetic disk, and the control means includes means for controlling the potential difference between the magnetic disk and the magnetic head slider applied by the voltage application means and stabilizing the state of the magnetic head slider in contact with the magnetic disk on the basis of the detection result of the detection means.
(2) The magnetic head includes a magnetic head for recording/reproducing information while flying above the magnetic disk with a predetermined spacing from the magnetic disk, and the control means includes means for controlling the potential difference between the magnetic disk and the magnetic head slider applied by the voltage application means and thus controlling the flying height of the magnetic head slider from the magnetic disk on the basis of the detection result of the detection means.
In the foregoing description, the position of the magnetic head slider and the driving force of the magnetic head represent the state of the magnetic head slider borne in air with a predetermined flying height for the air-bearing system, and the state of the magnetic head slider in contact with the surface of the magnetic disk by a predetermined contact force for the contact system.
(3) The detection means includes an acceleration detector.
(4) The control means operates in such a manner as to suppress the fluctuations of the position of the magnetic head slider and the fluctuations of the driving force of the magnetic head by controlling the potential difference applied by the voltage application means in accordance with the acceleration or the like of the disturbance detected by the detection means.
(5) Second detection means for detecting the roughness formed on the surface of the magnetic disk is further provided, and the control means controls the potential difference between the magnetic disk and the magnetic head slider applied by the voltage application means and thus controls at least selected one of the position of the magnetic head slider with respect to the magnetic disk and the driving force of the magnetic head in accordance with the roughness detected by the second detection means.
The magnetic head slider is made of an altic or the like conductive material. In the case where the magnetic head slider is made of a non-conductive material, a conductive film is formed on the slider surface opposed to the magnetic disk. This conductive film is formed with an insulating film of SiO2 or diamond-like carbon (DLC). An insulating layer may alternatively be formed on the surface of the magnetic disk. Upon application of a potential difference between the magnetic film on the magnetic disk and the magnetic head slider (or the conductive film on the slider surface) by the voltage application means, charges of opposite polarities are generated on the opposed surfaces of the magnetic film and the magnetic head slider, thereby generating an attractive force proportional to the square of the potential difference.
The air-bearing force is exerted by the dynamic pressure air-bearing mechanism on the magnetic head slider of the magnetic disk drive or the like, so that the magnetic head slider is kept in position flying above the surface of the magnetic disk rotating at high speed. The magnetic head slider can also be kept flying at a predetermined height by an attractive force (electrostatic attraction) equivalent to the air-bearing force generated between the magnetic head slider and the magnetic disk due to the potential difference applied by the voltage application means.
The dynamic system acting on the magnetic head slider is described below. Assume that Fa is the force generated by the dynamic pressure air-bearing mechanism, Fe is an electrostatic attractive force, Fn is a predetermined load exerted on the slider from the suspension supporting the slider, Fd is an external disturbance applied to the magnetic head slider and Fc is the contact force between the magnetic head and the magnetic disk for the contact system. Fa is inversely proportional to the square of the distance between the surface of the magnetic disk and the magnetic head slider, and proportional to the affected surface area S of the slider and the relative speed (peripheral speed) U between the magnetic disk and the magnetic head slider. Fe is proportional to the square of the potential difference V applied by the voltage application means, inversely proportional to the square of the distance between the surface of the magnetic disk and the magnetic head slider and proportional to the affected surface area S of the slider. Fd is the product of the equivalent mass m of the magnetic head and the disturbance acceleration a.
These relations are given by equations (1) to (9) below.
Fa==∈aUS/H2xe2x80x83xe2x80x83(1)
Fe==∈eV2S/H2xe2x80x83xe2x80x83(2)
Fn==∈fxe2x80x83xe2x80x83(3)
Fd=mxcex1xe2x80x83xe2x80x83(4)
Fa+Fcxe2x88x92Fexe2x88x92Fn+Fd=0xe2x80x83xe2x80x83(5)
Equation (5) is represents an equilibrium of forces, and equation (6) below is introduced from equations (1) to (4).
∈aUS/H2=∈eV2S/H2+∈fxe2x80x83xe2x80x83(6)
Solving this equation (6) about H, Fc and V, equations (7) to (9) are obtained.
H=[(∈aUxe2x88x92∈eV2)S/∈f]xc2xdxe2x80x83xe2x80x83(7)
Fc=(∈eV2xe2x88x92∈aU)S/H2+∈fxe2x88x92mxcex1xe2x80x83xe2x80x83(8)
V=[{(Fcxe2x88x92∈f+mxcex1)H2/S+∈aU}/∈e]xc2xdxe2x80x83xe2x80x83(9)
In these equations, ∈a, ∈e and ∈f are proportionality constants.
Equation (7) indicates that a change in voltage V changes the flying height H, equation (8) that a change in voltage V changes the contact force Fc, and equation (9) that a constant contact force Fc or a constant flying height H can be maintained by controlling the voltage V against the disturbance acceleration xcex1.
In the case where an inertial force is exerted due to a large disturbance acceleration or the like, the flying height or the contact force changes in accordance with equations (7) and (8), thereby causing an unstable reproduction signal. In view of this, a constantly stable signal reproduction is made possible by detecting the disturbance acceleration and applying a potential difference between the magnetic head and the magnetic disk by a feed-back circuit or by a feed-forward circuit in such a manner as to offset the inertial force in accordance with equation (9). The disturbance acceleration can be detected by detecting the acceleration directly, by detecting and differentiating the disturbance speed or by detecting and differentiating the displacement twice. In short, the quantity of state is detected and applied as a voltage to the magnetic head slider through a feed-back circuit or a feed-forward circuit thereby to reduce the inertial force due to the disturbance.
Also, a stable reproduction signal can be produced by detecting the quantities of state such as the displacement, speed, acceleration, etc., of the magnetic disk and by substituting an acceleration of inertia or calculating the fluctuation of flying height or the change in contact force directly, and then by applying a voltage to the magnetic head slider through the feed-back circuit or the feed-forward circuit in such a manner as to suppress the fluctuations of the flying height or the change in the contact force. Further, the load on the magnetic head due to the suspension or the like can be minimized by realizing a stabilized contact state of the contact system and a stabilized flying state of the air-bearing system. As a consequence, the service life of devices such as the magnetic head slider and the magnetic disk can be lengthened.
As described above, the magnetic disk drive according to the second magnetic disk drive of the invention can suppress the fluctuations of the position of the magnetic head due to the disturbances such as vibrations. In other words, the fluctuations of flying height of the magnetic head slider caused by disturbances can be suppressed for the air-bearing system, and the contact force fluctuations such as experienced when the magnetic head jumps up from the surface of the magnetic disk due to disturbances can be suppressed for the contact system. As a result, the instability of the write/read operations which otherwise might be caused by the disturbances can be prevented, with the result that a stabilized write/read signal characteristic can be secured against disturbances. Also, it is possible to suppress the fluctuations of the flying height or the fluctuations of contact force which are liable to occur due to the roughness of the surface of the magnetic disk. Consequently, the write/read signal characteristic can be prevented from becoming unstable due t6 the roughness of the magnetic disk surface, thereby making it possible to secure a stabilized write/read signal characteristic.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.